1. Field of the Invention
The present invention relates to a tilt sensor for detecting the tilting of a device such as a digital still camera. The invention also relates to a method for making such a tilt sensor.
2. Background of the Art
FIG. 15 illustrates an example of conventional tilt sensor (see JP-A-2007-139643). The illustrated tilt sensor X includes a mount board 91, a case 92, a cover plate 93, a pair of light receiving elements 94A and 94B, a light emitting element 95 and a rolling member 96. The case 92 includes a hollow which opens upward. The hollow is closed by the cover plate 93, whereby an inner space 92a is defined. The rolling member 96 is arranged to move freely by the pulling of gravity in the inner space 92a. The light receiving elements 94A, 94B and the light emitting element 95 are mounted on an obverse surface of the mount board 91. The light emitted from the light emitting element 95 is directed into the inner space 92a. Then, the light is reflected by a reflective film 93a provided on the cover plate 93. The rolling member 96 rolls within the inner space 92a in accordance with the change in posture of the tilt sensor X. In particular, the rolling member 96 can move to a position to conceal the light receiving element 94A, a position to conceal the light receiving element 94B, and a position to conceal the light emitting element 95. Depending on the position of the rolling member 96, the light emitted from the light emitting element 95 reaches only the light receiving element 94A, only the light receiving element 94B or does not reach the light receiving element 94A nor the light receiving element 94B. Thus, by monitoring the light reception by the light receiving elements 94A, 94B, the tilting within a plane including the obverse surface of the mount board 1 is detected.
To ensure accurate tilt detection, the rolling member should be arranged to move smoothly within the inner space 92a by gravity. However, in the conventional structure, the rolling member 96 may often adhere to the case 92 or the cover plate 93, thereby failing to shift position properly even when the pulling direction of gravity (relative to the sensor X) changes. This problem may occur more frequently as the size of the tilt sensor X is reduced.